Validation of the n-alkane technique to estimate intake, digestibility, and diet composition in sheep consuming mixed grain:roughage diets

Abstract

The usefulness of the n-alkane technique to estimate intake, digestibility, and diet composition in sheep fed mixed diets was tested in an experiment with 16 ewes consuming 4 different proportions of barley grain and straw ranging from 15:85 to 60:40. Two cases were considered: (1) straw as one component or (2) straw separated into leaves and stems. The relationship between estimated (Y) and observed (X) proportion of grain in the diet was highly significant (1: Y = 0.2355 + 0.9945X, r2 = 0.9999; 2: Y = –2.472 + 1.0063X, r2 = 0.9999). Actual intake was overestimated in (1) by 3.43–12.40%, the largest discrepancies corresponding to the lowest proportions of grain. In (2) actual intake was either overestimated (2.69%) or underestimated (5.38–6.85%), without a clear effect of the diet. A similar pattern was observed for digestibility, which was overestimated in (1) by 1.65–9.59% and overestimated, (by 2.07%) or underestimated (by 3.80–4.62%) in (2). Due to the small discrepancies between observed and estimated values, it may be concluded that the n-alkane technique might be a valid method for estimating intake, digestibility, and diet composition in sheep consuming mixed diets, for the two latter provided that faecal recovery of individual n-alkanes is calculated with enough accuracy.

The validity of n-alkanes to estimate intake and digestibility in Nellore beef cattle fed a tropical grass (Brachiaria brizantha cv. Marandu)

“…Recovery of natural alkanes was much lower than that observed in cattle fed temperate grasses Oliván et al, 2007), but similar to that recorded in tropical conditions (Hendricksen et al, 2002). The reasons for such differences may be sought in either animal/breed variability (Hendricksen et al, 2002;Valiente et al, 2003) or in the amount and structure of NDF. In this respect, it must be pointed out that the average concentration of cell wall in our forage was 680 g/g DM, a value well above that found in temperate lucerne hay by Oliván et al (2007) or Keli et al (2008) (472 and 463 g/kg DM, respectively), but below the NDF concentration found by Valiente et al (2003) in barley straw (816 g/kg DM).…”

“…Faecal recovery of natural alkanes increased with chain length, recoveries up to 77.0% (C 35 ), whereas dosed alkanes C 28 , C 32 and C 36 showed average recoveries of 94.2%, 97.2% and 86.8%, respectively. Increasing recovery of n-alkanes with chain length has also been observed by Mayes et al (1986b), Dove et al (2002), Valiente et al (2003) and Keli et al (2008), among others.…”

“…The reasons for such differences may be sought in either animal/breed variability (Hendricksen et al, 2002;Valiente et al, 2003) or in the amount and structure of NDF. In this respect, it must be pointed out that the average concentration of cell wall in our forage was 680 g/g DM, a value well above that found in temperate lucerne hay by Oliván et al (2007) or Keli et al (2008) (472 and 463 g/kg DM, respectively), but below the NDF concentration found by Valiente et al (2003) in barley straw (816 g/kg DM). These latter authors, however, recorded high long-chain n-alkane recoveries even in sheep fed 15:85 proportions of barley grain and straw.…”

“…Pellets were made weighing 6.5 g shredded papers and wrapping them in onionskin paper (about 1.5×4 cm). Six pellets were sampled in each experimental period and analysed for alkane concentration as described by Valiente et al (2003). Average alkane concentrations in the dosed pellets were 270.8±48.8 mg of C 28 , 290.4±47.1 mg of C 32 and 325.4±55.3 mg of C 36 in the first period, and 285.3±71.9 mg of C 28 , 301.8±75.3 mg of C 32 and 335.1±83.3 mg of C 36 in the second experimental period.…”

“…In this respect, it has been shown that either animal (species, breed, age, and size) or diet (feeding level and diet composition) factors may have an influence (Dillon and Stakelum, 1989;Dove et al, 1989Dove et al, , 2002Valiente et al, 2003;Giráldez et al, 2004;Ferreira et al, 2005;Oliván et al, 2007;Keli et al, 2008). Dove and Mayes (1991 stated that both n-alkane faecal recovery and within-day variation in the faecal concentration of dosed alkanes are more variable in cattle than in sheep.…”